﻿// OutputWindow.cs
//
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

namespace ICSharpCode.SharpZipLib.Zip.Compression.Streams
{

    /// <summary>
    /// Contains the output from the Inflation process.
    /// We need to have a window so that we can refer backwards into the output stream
    /// to repeat stuff.<br/>
    /// Author of the original java version : John Leuner
    /// </summary>
    public class OutputWindow
    {
        private static int WINDOW_SIZE = 1 << 15;
        private static int WINDOW_MASK = WINDOW_SIZE - 1;

        private byte[] window = new byte[WINDOW_SIZE]; //The window is 2^15 bytes
        private int windowEnd = 0;
        private int windowFilled = 0;

        /// <summary>
        /// Write a byte to this output window
        /// </summary>
        /// <param name="abyte">value to write</param>
        /// <exception cref="InvalidOperationException">
        /// if window is full
        /// </exception>
        public void Write(int abyte)
        {
            if (windowFilled++ == WINDOW_SIZE)
            {
                throw new InvalidOperationException("Window full");
            }
            window[windowEnd++] = (byte)abyte;
            windowEnd &= WINDOW_MASK;
        }


        private void SlowRepeat(int repStart, int len, int dist)
        {
            while (len-- > 0)
            {
                window[windowEnd++] = window[repStart++];
                windowEnd &= WINDOW_MASK;
                repStart &= WINDOW_MASK;
            }
        }

        /// <summary>
        /// Append a byte pattern already in the window itself
        /// </summary>
        /// <param name="len">length of pattern to copy</param>
        /// <param name="dist">distance from end of window pattern occurs</param>
        /// <exception cref="InvalidOperationException">
        /// If the repeated data overflows the window
        /// </exception>
        public void Repeat(int len, int dist)
        {
            if ((windowFilled += len) > WINDOW_SIZE)
            {
                throw new InvalidOperationException("Window full");
            }

            int rep_start = (windowEnd - dist) & WINDOW_MASK;
            int border = WINDOW_SIZE - len;
            if (rep_start <= border && windowEnd < border)
            {
                if (len <= dist)
                {
                    System.Array.Copy(window, rep_start, window, windowEnd, len);
                    windowEnd += len;
                }
                else
                {
                    /* We have to copy manually, since the repeat pattern overlaps. */
                    while (len-- > 0)
                    {
                        window[windowEnd++] = window[rep_start++];
                    }
                }
            }
            else
            {
                SlowRepeat(rep_start, len, dist);
            }
        }

        /// <summary>
        /// Copy from input manipulator to internal window
        /// </summary>
        /// <param name="input">source of data</param>
        /// <param name="len">length of data to copy</param>
        /// <returns>the number of bytes copied</returns>
        public int CopyStored(StreamManipulator input, int len)
        {
            len = Math.Min(Math.Min(len, WINDOW_SIZE - windowFilled), input.AvailableBytes);
            int copied;

            int tailLen = WINDOW_SIZE - windowEnd;
            if (len > tailLen)
            {
                copied = input.CopyBytes(window, windowEnd, tailLen);
                if (copied == tailLen)
                {
                    copied += input.CopyBytes(window, 0, len - tailLen);
                }
            }
            else
            {
                copied = input.CopyBytes(window, windowEnd, len);
            }

            windowEnd = (windowEnd + copied) & WINDOW_MASK;
            windowFilled += copied;
            return copied;
        }

        /// <summary>
        /// Copy dictionary to window
        /// </summary>
        /// <param name="dict">source dictionary</param>
        /// <param name="offset">offset of start in source dictionary</param>
        /// <param name="len">length of dictionary</param>
        /// <exception cref="InvalidOperationException">
        /// If window isnt empty
        /// </exception>
        public void CopyDict(byte[] dict, int offset, int len)
        {
            if (windowFilled > 0)
            {
                throw new InvalidOperationException();
            }

            if (len > WINDOW_SIZE)
            {
                offset += len - WINDOW_SIZE;
                len = WINDOW_SIZE;
            }
            System.Array.Copy(dict, offset, window, 0, len);
            windowEnd = len & WINDOW_MASK;
        }

        /// <summary>
        /// Get remaining unfilled space in window
        /// </summary>
        /// <returns>Number of bytes left in window</returns>
        public int GetFreeSpace()
        {
            return WINDOW_SIZE - windowFilled;
        }

        /// <summary>
        /// Get bytes available for output in window
        /// </summary>
        /// <returns>Number of bytes filled</returns>
        public int GetAvailable()
        {
            return windowFilled;
        }

        /// <summary>
        /// Copy contents of window to output
        /// </summary>
        /// <param name="output">buffer to copy to</param>
        /// <param name="offset">offset to start at</param>
        /// <param name="len">number of bytes to count</param>
        /// <returns>The number of bytes copied</returns>
        /// <exception cref="InvalidOperationException">
        /// If a window underflow occurs
        /// </exception>
        public int CopyOutput(byte[] output, int offset, int len)
        {
            int copy_end = windowEnd;
            if (len > windowFilled)
            {
                len = windowFilled;
            }
            else
            {
                copy_end = (windowEnd - windowFilled + len) & WINDOW_MASK;
            }

            int copied = len;
            int tailLen = len - copy_end;

            if (tailLen > 0)
            {
                System.Array.Copy(window, WINDOW_SIZE - tailLen, output, offset, tailLen);
                offset += tailLen;
                len = copy_end;
            }
            System.Array.Copy(window, copy_end - len, output, offset, len);
            windowFilled -= copied;
            if (windowFilled < 0)
            {
                throw new InvalidOperationException();
            }
            return copied;
        }

        /// <summary>
        /// Reset by clearing window so <see cref="GetAvailable">GetAvailable</see> returns 0
        /// </summary>
        public void Reset()
        {
            windowFilled = windowEnd = 0;
        }
    }
}